API System

By

Dr. Nabil El Aila

Assistant Professor of Molecular Microbiology

Medical Technology Department

Al -Aqsa University

API System

• The analytical profile index or API is a

classification of bacteria based on experiments,

allowing fast identification. This system is developed

for quick identification of clinically relevant bacteria.

Because of this, only known bacteria can be

identified.

API® Gram negative Identification

• API 20E – 18-24 hour identification of Enterobacteriacae and

other non-fastidious gram negative bacteria

• API Rapid 20E – 4-hour identification of Enterobacteriaceae

• API 20NE – 24 to 48-hour identification of Gram negative

non-Enterobacteriaceae

• API NH – 2-hour identification of Neisseria Haemophilus and

Branhamella catarrhalis

• API Campy – 24-hour identification of Campylobacter species

API® Gram positive Identification

• API Staph – Overnight identification of clinical staphylococci

and micrococci

• RAPIDEC® Staph – 2-hour identification of the commonly

occurring staphylococci

• API 20 Strep – 4 or 24-hour identification of streptococci and

enterococci

• API Coryne – 24-hour identification of Corynebacteria and

coryne-like organisms

• API Listeria – 24-hour identification of all Listeria species

Other API System

API® Anaerobe Identification

• API 20A® – 24-hour identification of anaerobes

• Rapid ID 32A – 4-hour identification of anaerobes

API® Yeast Identification

• API 20C AUX – 48 to 72-hour identification of yeasts

Others

• API® 50 CH – Performance of carbohydrate metabolism tests

• API ZYM® – Semiquantitation of enzymatic activities

API 20E

• The API 20E Strip, For Identification Of The

Enterobacteriaceae and other Gram negative rods,

Consists of 20 microtubules containing dehydrated

substrates.

• These tests are inoculated with a bacterial suspension

that reconstitute the media.

•

During incubation, the metabolism of the organism

produces color changes that are either spontaneous or

revealed by the addition of reagent.

API 20E

• API 20E are contained in an aluminum pouch. Once

opened the pouch should be re-sealed using the clip

seal supplied with the kit.

• The strips may then be kept for up to 10 months at 2-

8 C

or untill the expiry date indicated on the

packaging.

• Reagent used in this procedure should also be strored

at 2 -8 C

and before their expiry date.

API 20E reagent

• TDA reagent (API 70 400)

• James reagent (API 70 540)

• VPI reagent (API 70 420)

• VP2 reagent ( API 70 430)

API 20E Procedure

• prepare an incubation tray and lid and distribute 5 ml

of sterile distilled water into the tray to create a

humid chamber.

• Record the strain reference on the tab of the tray.

• Place the API 20 E strip in the tray.

• Using a sterile disposable loop remove a single well-

isolated colony from an isolation plate and carefully

emulsify this in 5 ml of sterile distilled water.

API 20E Procedure

• With a sterile disposable pipette fill both the tube and

cupule of the test CIT, VP and GGL with the bacterial

suspension.

• Using same pipette fill only the tubes of the other test.

• Create anaerobic conditions in the tests ADH , LDC ,

ODC , URE and H2S by overlaying with mineral oil.

• Inoculate and streak MacConkey agar plate.

API 20E Procedure

• place a lid on the incubation tray and incubate

both the strip and the MacConkey plate at 37

C

for 18 – 24 hours.

Interpretation

• Check the MacConkey purity plate to ensure.If the culture is mixed repeat the test

• The following tests require the addition of reagent as follows:

- Vp test: add one drop of VPI and VP2 reagent

and wait for ten min for colour development.

- TDA test: add one drop of TDA reagent.

- IND test: add one drop of James reagent.

Interpretation

• Read the API strip according to the interpretation

table, and record the result on the report sheet.

• On the report shhet, the test are separated into groups

of three and number 1 , 2 or 4 is allocated for each

test. By adding the numbers corresponding to the

positive reaction within each groupe, a7- digit profile

number is obtained for 20 tests of the API 20E strip.

Interpretation

• The 7- digit profile is then compared with the

numerical profile in the API 20 E analytical

profile index book to obtain the organism

identification.

All-negative tests

All-positive tests

API 20E

READING THE API 20

TESTS SUBSTRATE REACTION TESTED - RESULTS

*negative*

+ RESULTS

*positive*

ONPG ONPG beta-galactosidase colorless yellow

ADH arginine arginine dihydrolase yellow red/orange

LDC lysine lysine decarboxylase yellow red/orange

ODC ornithine ornithine decarboxylase yellow red/orange

CIT citrate citrate utilization pale green/yellow blue-green/blue

H2S Na thiosulfate H2S production colorless/gray black deposit

URE urea urea hydrolysis yellow red/orange

TDA tryptophan deaminase yellow brown-red

IND tryptophan indole production yellow red (2 min.)

VP Na pyruvate acetoin production colorless pink/red (10 min.)

GEL charcoal gelatin gelatinase no diffusion of black black diffuse

GLU glucose fermentation/oxidation blue/blue-green yellow

MAN mannitol fermentation/oxidation blue/blue-green yellow

INO inositol fermentation/oxidation blue/blue-green yellow

SOR sorbitol fermentation/oxidation blue/blue-green yellow

RHA rhamnose fermentation/oxidation blue/blue-green yellow

SAC sucrose fermentation/oxidation blue/blue-green yellow

MEL melibiose fermentation/oxidation blue/blue-green yellow

AMY amygdalin fermentation/oxidation blue/blue-green yellow

ARA arabinose fermentation/oxidation blue/blue-green yellow

OX oxidase oxidase colorless/yellow violet

Triad I II III IV V VI VII

Tube

oxid

ase

Reaction

- - -

-

- - -

- -

-

Point

Add

7-digital

Code

API 20E

• QUALITY CONTROL

• Refer to laboratory Quality Control Manual for all

Quality Control procedure.

• SAFETY

• Standard microbiological technique should be used in

the performance of this test. After use, the strips

should be placed in red plastic disposal bag.

API 20E Limitations

• The API 20 E system is intended for the identification

of those non-fastidious , Gram negative rods included

in the analytical profile index and exclusively for

them. It cannot be used to identify any other organism

or to exclude their presence.

• Interpretation of the test result should be made by

competent microbiology technologist.

• Any difficulties with interpretation should be

referred to a Senior Technologist or Supervisor.

API 20 NE reading table

All-negative tests

All-positive tests

API 20 Strep reading table

All-positive tests

All-negative tests

API 20 Staph reading table

All-positive tests

All-negative tests

All-positive tests

All-negative tests

API 20 A reading table

API NH reading table